Abstract
A systematic study of particle identification performance of full-scale dE/dx sampling detectors including large drift was realized in a device containing 64 pairs of 2 × 2 cm2 proportional cells and a 50 cm drift space. Gas, pressure and drift dependence of the relativistic rise of ionization and mass resolution were measured from 0.5 to 5.5 atm at 15 GeV/c, for mixtures of argon and CH4, C2H4, C2H6, C3H8, iC4H10, CO2, CO2/C2H6, Xe/CH4, Xe/C2H6. Multitrack resolution (linearity of dE/dx response, saturation) was measured for up to 10 quasi-simultaneous particles within a 2 cm diameter beam spot during 1 μs fast spill. The amplitude resolution was found to improve more slowly with pressure (7.5% FWHM was reached at 5.5 atm for 14 m NTP equivalent detector length) than expected from extrapolations of atmospheric pressure measurements without drift. Pressure dependence of signal attenuation in the drift space was smallest in Ar + CH4 mixtures. The results confirm a marked reduction of the relativistic rise slope at higher pressures.
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